1. Field of Industrial Application
The present invention relates to a method and apparatus for forming a cylindrical closed-end preform which can be used to blow mold a synthetic resin vessel. More particularly, the present invention concerns a method and apparatus for injection molding a preform having a crystallized neck by utilizing a neck cavity mold in the injection molding step.
2. Description of the Prior Art
There is known a particular method of molding a heat-resistant bottle by crystallizing a non-orientated or extremely low-orientated area of the bottle or a preform used to form the bottle, which is called a neck or mouth portion. Such a method has been practiced particularly for bottles of polyethylene terephthalate (PET) which have been used to receive high-temperature materials.
In such neck crystallization, heaters are disposed around the neck of a bottle (or a preform) to be crystallized, for example, in such a manner as disclosed in Japanese Patent Publication No. Sho 62-25491.
The neck thus crystallized is easy to be deformed, for example, thermal distortion and heat shrinkage. There are thus raised many problems in that for obtaining high-quality products, an operator skilled in the art must set the injection molding conditions of preforms, control the quality of products (bottles or preforms) to be stored and design the necks under forecast of the shrinkage thereof. Therefore, small-scale manufacturers could not take this method. In this connection, the necks are required to have higher dimensional accuracy in many standards to prevent the leakage therethrough.